Cytochrome c is an essential component for mediating electron transfer between the primary dehydrogenases and the terminal oxidase for the oxidation of substrate with reduction of molecular oxygen to H.sub.2 O. This electron transfer reaction is based on an oxidation-reduction of the heme iron. Recently attempts have been made to apply the electron transfer reaction of cytochrome c as new materials imitating biological materials or elements, namely biochips; e.g. by using cytochrome c.sub.552 of Hydrogenobacter thermophilus (Kodama et al., U.S. Pat. No. 5,459,046). Acetic acid bacteria including Gluconobacter and Acetobacter possess highly efficient ability for sugar- and sugar alcohol-oxidation and are industrially used for producing vinegar and L-sorbose which is used as intermediate of vitamin C production. In oxidative fermentation, cytochrome c plays an important role to complete the oxidation. Cytochrome c proteins have been purified and characterized from many organisms, including Gluconobacter; e.g. Matsushita et al. reported the purification of CO-binding cytochrome c.sub.553 (CO) (molecular weight, 48 kDa) from Gluconobacter suboxydans (FEMS Microbiol. Lett., 10:267-270, 1981) and later the cytochrome c.sub.553 (CO) was found to be identical to the second subunit of alcohol dehydrogenase of Gluconobacter. Amplification of the cytochrome c.sub.553 (CO) in an alcohol dehydrogenase second subunit-deficient Gluconobacter slightly improved L-sorbose production from D-sorbitol in its specific rate (g-product per g-cell-hour) as disclosed in J. Ferment. Bioeng., 74, 209-213, 1992 (Y. Takeda et al.). In addition to the cytochrome c.sub.553, cytochrome c.sub.551 (AL) (molecular weight 55 kDa) and cytochrome c.sub.551 (CO) (molecular weight 72 kDa) [Ameyama et al., Agri. Biol. Chem. 51, 2943-2950 (1987)] were also isolated from Gluconobacter. The cytochrome c.sub.551 (AL) is one of the subunits of aldehyde dehydrogenase of Gluconobacter suboxydans consisting of two subunits; the other subunit is primary aldehyde dehydrogenase of 86 kDa. AL in cytochrome c.sub.551 (AL) stands for "aldehyde".